Archive for the ‘New Zealand News’ Category

Mt Tongariro – long considered a peaceful neighbour to the rowdy Ruapehu – is much more fiery than we ever realised, says a scientist sharing new findings today.

GNS Science volcanologist Brad Scott, among scientists giving presentations in a workshop at Whakapapa Village, has found evidence of eruptions at Mt Tongariro that weren’t previously on the records.

Tongariro’s dramatic eruptions in August and November of 2012 transformed our understanding of what had been considered a comparatively docile mountain, Mr Scott said.

When ash shot from the Te Maari Crater 7km into the sky shortly before midnight on August 6, it was thought at the time to have been the first blow there since 1896.

But Mr Scott has since found records indicating an eruption at the crater in 1928, with other events at Red Crater – a feature of the Tongariro Alpine Crossing – in 1909, 1926, 1927 and 1934. Further, there was volcanic unrest at the mountain right up until the 1970s, he said.

“We all knew Ruapehu and Ngauruhoe were pretty busy but, until now, nobody really perceived Tongariro as being as active as it has been.”

The new information, with the 2012 eruptions, had led to a range of new protocols and emergency policies at the peak, including warning systems and more public information. “[And] we’ve upgraded monitoring equipment in the area and have put in place more seismographs.”

Other research being presented would discuss findings around the ballistics of rocks that were ejected from the mountain in 2012, as well as the volcanic avalanches and debris flows that came with the eruption.

Mr Scott saw the event as a success story because authorities had been able to warn residents after monitoring picked up elevated activity.

Today’s workshop will kick off a weekend reflecting on the 20th anniversary of the 1995-96 eruptions of Mt Ruapehu. This year also marks the 40th anniversary of the 1975 Ngauruhoe eruption and the 70th anniversary of the 1945 Ruapehu eruption.

Mt Ruapehu eruptions: 20 years on

• The 1995-96 eruptions ejected a total of 60 million cubic metres of acidic ash – blanketing districts up to 300km from the mountain, irritating eyes and throats in the central North Island, damaging car paintwork and machinery, contaminating rivers and water supplies, ruining crops, closing state highways, forcing airports to shut and killing livestock which ate ash-covered pastures.

• Electricity suppliers were hit with multimillion-dollar losses as ash shorted out power pylons and severely damaged turbines in the Rangipo power station. At times the ash plume reached as high at 10km, which represented a significant aviation hazard.

• The eruptions were similar in size to those in 1945, but their social and economic impacts were much greater. In 1945 there was just one ski area and no ski lifts on Ruapehu. By 1995, there were three ski areas and 36 ski lifts. By the mid-90s there were up to 10,000 people on the mountain on some days during winter.

Rangitoto may be much older – and more explosive – than previously believed.

A new study has led scientists to reassess how volcanoes may behave in the future and could be a large step toward unlocking Auckland’s mysterious volcanic past.

Contrary to the long-held belief that Rangitoto was formed less than 700 years ago and has erupted only twice, University of Auckland researchers now suspect there may have been intermittent activity from between 1500 years ago to 500 years ago.

Alongside basaltic ash from the island volcano’s most recent eruption between 500 and 550 years ago, sediment samples taken from Lake Pupuke have revealed evidence of minor eruptions 922 years ago, 1040 years ago and 1500 years ago.

A new discovery that shows that Rangitoto erupted “semi-continuously” for about 1000 years is prompting scientists to re-think what the volcano could do in the future.

The most recent volcano to erupt in Auckland, Rangitoto was thought to be close to 550-years-old and to have erupted once or twice in its lifetime.

However, new University of Auckland research shows that the volcano actually erupted “intermittently” or “semi-continuously” from about 1500 years to 500 years ago, smashing traditionally-held beliefs about volcanoes here and around the globe.

The findings are also prompting scientists to re-think how Auckland’s volcanoes will behave in the future.

“The old paradigm was that these volcanoes erupt suddenly in a new location each time, and only live for months to a year or two,” said lead researcher Associate Professor Phil Shane.

White Island is continuing to produce “vigorous bursts” of mud, rock steam and gas up to 100m high and larger explosions including molten sulphur are possible, say experts.

The seismic activity, which has lasted several days, poses a greater than usual risk to visitors, said GNS Science.

Scientists monitoring the island volcano in the Bay of Plenty say the crater lake is drying out and the frequent bursts of mud, steam and gas were still vigorous.

Past monitoring of the island showed new eruptions often develop from this type of activity and small muddy lakes sometimes form in craters “as the unrest develops geysering and explosions occur through these lakes, becoming more vigorous with time”.

White Island
This week downgraded from alert level two to one (out of five). A recently-established lava dome has stopped growing, but scientists say a column of magma not far beneath still poses a threat.

Mt Ruapehu
Remains at alert level one with an exclusion zone around the summit. A suspected blockage below the crater lake may be causing a gas build up that could result in sudden eruption.

Mt Tongariro
Remains at alert level one with part of the Tongariro Alpine Crossing closed. Emitting large amounts of gas and sulphur dioxide and scientists still expect a repeat of the last eruption in November.

Just like Mt Tongariro’s surprise bang on Wednesday afternoon, what happened a few kilometres away at 8.20pm on September 25, 2007, came suddenly and violently.

Shortly before airline pilots noticed a black plume rising above Mt Ruapehu, a volcanic blast threw ash, rocks and water across the summit area, sending two muddy torrents down the skifields.

Inside a hut on the edge of the crater lake, William Pike and James Christie heard a “massive boom” before the building’s door was blown from its hinges and mud and rock poured inside. Mr Pike’s crushed leg later had to be amputated.

The warning signs Mt Ruapehu gave in the days before that explosive moment are being seen again now – worrying scientists that the mountain could be about to produce a similar-sized eruption.

GNS volcanologist Michael Rosenberg said Mt Ruapehu has been showing two forms of unrest, which are considered unrelated.

There have been 45 earthquakes about 5km beneath the mountain since early August, but 35 of those have come in the past month.